1. Field of the Invention
The present invention relates, generally, to torsional-vibration dampers for motor vehicles.
2. Description of the Related Art
A torsional-vibration damper is, generally, a type of elastic coupling disposed between two components of a drive train of a vehicle, for example, between an internal-combustion engine and a transmission. Such devices reduce or otherwise prevent vibrations from being transmitted from the engine to other parts of the drive train.
The basic embodiment of a torsional-vibration damper includes a primary element and a secondary element that can be coupled to each other by a spring device and are limited in movement in relation to each other about a rotational axis. The spring device advantageously includes a plurality of springs disposed on a radial arc spaced relative to the rotational axis and, preferably, at a certain uniform distance from each other. The springs, or a sequence of multiple springs, if applicable, are then connected to the primary element on one side of the springs and to the secondary element on the other side of the springs. Torque is transmitted through the spring coupling, and, as a result of the spring characteristic, a certain additional damping effect is achieved.
When torsional-vibration dampers are used in the drive train, however, it is necessary to have a high moment of friction in the drive train to decrease the vibration amplitudes in the resonance range. Unfortunately, this causes the transmission characteristic to deteriorate in higher speed range.
In response to this problem a torsional-vibration damper has been developed in the related art that includes primary and secondary elements coupled not only by the spring device, but additionally via a friction device whose damping effect can be controlled and adjusted by a special force-generating device. The friction device can also be engaged and disengaged in the manner of a clutch.
Although the torsional-vibration dampers known in the related art are basically effective in solving this problem, they have distinct disadvantages. In particular, they are often physically complex and also require a separate control system. The control system operatively controls the friction device to selectively provide the desired controlled moment of friction given the specific operating conditions at the time. The inherent complexity of both the friction device and its control system results in a torsional-vibration damper that can be cost prohibitive. Therefore, the manufacturing costs of many such devices are considered too high for many applications.
Thus, there remains a need in the art for a torsional-vibration damper having a friction device that provides a controlled moment of friction. In particular, there remains a need in the art for torsional-vibration damper that employs a simple friction device to provide a damping effect that does not need a separate control system and can be produced cost-effectively.